The present invention relates to a sheet-fed rotary printing press with a convertible mechanism, which performs switching between single-sided printing and double-sided printing by using a convertible cylinder with a gripper unit and holding member on its outer surface.
In general, a sheet-fed rotary printing press with a convertible mechanism has a convertible cylinder, and a gripper unit comprised of a plurality of pairs of grippers and gripper pads, and a holding member are provided to the outer surface of the convertible cylinder. U.S. Pat. No. 4,823,695 discloses a three-cylinder-type sheet-fed rotary printing press with a sheet turn-over apparatus or convertible mechanism, which has a transfer cylinder, a turn-over or convertible cylinder, and a double-diameter cylinder between them. This printing press will be described in detail. The turn-over cylinder has a plurality of grippers (A) for gripping the leading edge of a sheet fed from the double-diameter cylinder during single-sided printing to allow conveyance, and a plurality of grippers (B) for holding the trailing edge of the sheet fed from the double-diameter cylinder and performing gripping change of the sheet to the grippers (A) during double-sided printing.
In this arrangement, during double-sided printing, the trailing edge of the sheet gripped by the grippers of the upstream double-diameter cylinder is gripped by the grippers (B) of the turn-over cylinder when it is located at a position opposing the convertible cylinder. Simultaneously, the grippers of the double-diameter cylinder are opened, so the sheet is transferred to the turn-over cylinder. Subsequently, the grippers (B) and (A) of the turn-over cylinder move such that their gripper ends become close to each other, and open and close at momentary different timings, so the trailing edge of the sheet is gripping-changed from the grippers (B) to the grippers (A). Then, the grippers (A) and (B) move in the opposite directions to reverse the sheet gripped by the grippers (A). When the trailing edge of the sheet is located at a position opposing a downstream impression cylinder, the sheet is gripping-changed from the grippers (A) to the grippers of the downstream impression cylinder. After that, the lower surface of the sheet is printed by a downstream printing unit.
In the conventional sheet-fed rotary printing press with the convertible mechanism, the plurality of grippers (B) are arranged almost equidistantly in the axial direction. However, as the widthwise sizes of the sheets sometimes differ depending on the sheet sizes, the two sides of the sheet do not correspond to the positions of the grippers (B), and are not gripped by the grippers (B).
In this case, as the grippers (B) and (A) rotate along loci with small radii of curvature, sometimes gripping change cannot be performed. When gripping change is to be performed from the grippers (B) to the grippers (A), as the peripheral velocity of the grippers (B) is fast, the two sides of the sheet which are not gripped by the grippers (B) flutter as if they wave. Due to this fluttering, the two sides of the sheet are not smoothly guided to the grippers (A), and the sheet cannot be gripping-changed to the grippers (A). Also, the leading edge portions of the two sides of the sheet abut against the grippers (A), and accordingly the corner of the sheet is bent, or a registration error occurs.
It is an object of the present invention to provide a sheet-fed rotary printing press with a convertible mechanism, which can transfer a sheet reliably.
It is another object of the present invention to provide a sheet-fed rotary printing press with a convertible mechanism, in which damage to the sheet is prevented.
It is still another object of the present invention to provide a sheet-fed rotary printing press with a convertible mechanism, in which a registration error is prevented.
In order to achieve the above objects, according to the present invention, there is provided a sheet-fed rotary printing press with a convertible mechanism, comprising a convertible cylinder for conveying a sheet-like object, a plurality of first gripper units arranged on an outer surface of the convertible cylinder and lined up in an axial direction of the convertible cylinder, and adapted to grip the sheet-like object, a plurality of holding members arranged on the outer surface of the convertible cylinder to be adjacent to the first gripper units, and lined up in the axial direction of the convertible cylinder to be phase-shifted from the first gripper units, a convey mechanism which, in single-sided printing, conveys the sheet-like object fed from an upstream convey cylinder by gripping a leading edge thereof upon opening/closing operation of the first gripper units, and in double-sided printing, holds a trailing edge of the sheet-like object fed, from the upstream convey cylinder, with the holding members and thereafter gripping-changes the sheet-like object to the first gripping units, and a pair of guide members arranged at at least one of a position between the holding members and an outermost position outside the holding members, and adapted to guide two sides of the sheet-like object conveyed by the holding members to corresponding ones of the first gripper units.